Original Article
http://dx.doi.org/10.1590/2317-6431-2014-1533
Audiological profile of agricultural drivers exposed to noise and hydrocarbons Perfil audiológico de motoristas agrícolas expostos: ruído e hidrocarbonetos Renata Fernandes1, Miriam Harumi Tsunemi2, Fernanda Zucki3
ABSTRACT
RESUMO
Purpose: To establish the audiological profile of agricultural drivers
Objetivo: Estabelecer o perfil audiológico de motoristas agrícolas ex-
simultaneously exposed to noise and hydrocarbons. Methods: The
postos, simultaneamente, a ruído e hidrocarbonetos. Métodos: Foram
study comprised analysis of the medical records of agricultural drivers
analisados os prontuários de motoristas com queixas auditivas de uma
with hearing complaints, from an agricultural company of Lençóis
empresa do ramo agrícola do município de Lençóis Paulista (SP), dentro
Paulista (SP), Brazil, within the Environmental Risk Prevention Program.
do Programa de Prevenção de Riscos Ambientais (PPRA). As informa-
The information analyzed included age, period of simultaneous exposure
ções analisadas foram: idade, tempo de exposição combinada a ruído e
to noise and hydrocarbons and testing of reference pure tone audiometry.
hidrocarbonetos e exames de audiometria tonal liminar de referência.
Survival models for grouped data (proportional risk and logistic) were
Para a análise da influência da idade e do tempo de exposição sobre os
adjusted to analyze the influence of age and period of exposure of
limiares auditivos, ajustaram-se modelos de sobrevivência para dados
hearing thresholds. Results: It was observed that the effects of age
grupados (riscos proporcionais e logísticos). Resultados: Verificou-se
and period of simultaneous exposure to noise and hydrocarbons were
que os efeitos da idade e do tempo de exposição combinada a ruído e
significant for hearing loss in proportional risk and logistic models.
hidrocarbonetos foram significativos na perda de audição, nos modelos
Conclusion: It is fundamental to develop actions for the prevention
de riscos proporcionais e logísticos. Conclusão: É fundamental o de-
of hearing loss in agricultural drivers exposed to the agents noise and
senvolvimento de ações voltadas para a prevenção de perdas auditivas
hydrocarbons.
em motoristas agrícolas expostos aos agentes ruído e hidrocarbonetos.
Keywords: Noise; Hearing; Occupational exposure; Chemical com-
Descritores: Ruído; Audição; Exposição ocupacional; Compostos quí-
pounds; Hidrocarbons
micos; Hidrocarbonetos
This study was conducted at Instituto Alfa de Comunicação e Audição, Bauru (SP), Brazil. (1) Specialization in Clinical Audiology, Instituto Alfa de Comunicação e Audição, Bauru (SP), Brazil. (2) Biostatistics Department, Universidade Estadual Paulista “Júlio de Mesquita Filho” – UNESP – Botucatu (SP), Brazil. (3) Speech Pathology Department, Bauru School of Dentistry, Universidade de São Paulo – USP – Bauru (SP), Brazil. Conflict of interests: No Authors’ contribution: RF chief investigator, study design, schedule design, literature review, data collection, paper writing, submission and processing; MHT adjunct investigator, statistical analysis of data, aid in paper writing; FZ supervisor, study design, schedule design, data analysis, correction of paper writing, approval of final version. Correspondence address: Renata Fernandes. R. Raposo Tavares, 312, Jardim Ubirama, Lençóis Paulista (SP), CEP: 18683-510, Brazil. E-mail:
[email protected] Received on: 1/18/2015; Accepted on: 10/26/2015
Audiol Commun Res. 2015;20(4):313-20
313
Fernandes R, Tsunemi MH, Zucki F
INTRODUCTION Hearing loss is an occupational disease and, even though it may be prevented, it is considered an important health problem in our society. Despite the higher prevalence in industrialized countries, in Brazil, the noise-induced hearing loss (NIHL) is among the main health problems of workers(1). Workers affected by hearing loss are subjected to social isolation, impairing the communication with family and friends, reducing the ability to monitor the working environment (caution signs), increasing the risk of accidents in the workplace and reducing the quality of life, due to the inflexible tinnitus(2). Therefore, the Ministry of Work(3) and the Guideline SSST/ MTb n. 5, published in February 25th 1997(4), established minimum guidelines and parameters for the evaluation and follow-up of hearing in workers exposed to high sound pressure levels. The NIHL has been defined as a sensorineural change in hearing thresholds caused by exposure to occupational noise, presenting as main characteristics the irreversibility and gradual progression, according to the period of exposure. It is known that, besides noise, some chemicals used in several industrial fields may also lead to hearing loss, and when there is co-exposure – chemical combined with noise – the hearing loss may be greater(5,6). The synergic interaction between noise and solvents has been described in some studies(7,8), while others demonstrated that noise is dominant with regard to occupational hearing loss(9,10). According to the National Institute for Occupational Safety and Health (NIOSH) (11), three groups are considered high priority for research: solvents, asphyxiating agents and metals, and more recently the organophosphate pesticides(12). This study highlighted the effects of combined exposure of hydrocarbons and noise. Investigations on the effects of hydrocarbon on the auditory system, as well as the harmful effects of simultaneous exposure to more than one agent, such as noise, are still scarce. The audiological findings of hearing loss due to occupational exposure to chemicals are not very different from NIHL concerning the audiometric configuration. In general, this loss is characterized as being cochlear, bilateral, symmetric, progressive and irreversible, with onset in high frequencies, being nearly identical to NIHL(13). The toxic action of chemicals on the auditory system may be peripheral or central, ranging from lesions to external ciliated cells to lesions of the 8th cranial nerve, changes in the vestibular system and central nervous system(14). Petroleum is a complex mixture containing several compounds, mostly represented by hydrocarbons. According to its origin, chemical compositions and physical properties, there is variation from an oil field to another. The compounds of interest that require greater environmental concern are benzene, toluene, ethylbenzene and xylene. These compounds, also known as BTEX, are defined as monoaromatic hydrocarbons, 314
whose molecular structures are primarily characterized by the presence of a benzene ring. They are mainly used in solvents and fuels, being the most soluble constituents of gasoline. These compounds are toxic for both the environment and mankind, depressing the central nervous system and presenting chronic toxicity(15). Studies demonstrated that the site of the lesion, mechanisms and extension of the disorder caused by these toxins may vary according to the risk factors, which include the type of contaminant, interactions with other ototoxic agents, concentration and period of exposure(16). Findings of ototoxicity caused by exposure to chemicals demonstrated the need to broaden the discussion on assessment of the auditory risk and adoption of preventive measures for application in workers simultaneously exposed to certain agents. International laws do not consider as mandatory the monitoring of hearing of workers exposed to chemical products, unless exposure occurs at noise levels above the allowed limits. In Brazilian work laws there is no recommendation for the regular accomplishment of audiometry in workers exposed to chemical products, except for those exposed to noise according to annexes I and II of NR-15(17). The Decree 3048 of Social Security(18) acknowledges benzene and its toxic homologues (toluene and xylene) and aliphatic or aromatic hydrocarbons (their toxic halogenated derivatives) as etiological agents or risk factors for hearing loss of occupational origin. This decree indicates that exposures to these agents should be considered when assessing a hearing loss and the workplace conditions. However, the decree only acknowledges the causal relationship, and does not establish conditions for prevention. Therefore, this study analyzed the audiological profile of agricultural drivers simultaneously exposed to noise and hydrocarbons.
METHODS This study was approved by the Institutional Review Board of Bauru School of Dentistry, Universidade de São Paulo (protocol n. 488.758) and was conducted upon acceptance of the participating company. Study design This was an analytical cohort prospective study, characterized by a non-probabilistic sample, based on collection of data from the records of workers in an agricultural company from the interior of São Paulo State, based on the Environmental Risk Prevention Program (PPRA). Inclusion criteria and sample selection The inclusion criteria adopted for sample selection were the Audiol Commun Res. 2015;20(4):313-20
Hearing: Noise and hydrocarbons
simultaneous exposure to noise and hydrocarbons, besides the presence of hearing complaints. The records of 25 drivers meeting the inclusion criteria were selected in November and December 2013. The age of workers ranged from 21 to 54 years, with mean age of 37.8 years (±9.81). The period of combined exposure to noise and hydrocarbon was 6 to 20 years, with mean exposure of 8.5 years (±7.04).
on the statistics that maximizes the likelihood to identify this true model, more specifically, BIC=-2L + 2 k ln (n), in which L is the natural logarithm of the maximum likelihood function, k is the number of parameters and n is the number of observations. The model with lower BIC value presents the best adjustment(21). The degree of hearing loss was determined by the scoring proposed by the World Health Organization(20), which considers the mean frequencies of 500, 1000, 2000 and 4000 Hz (Chart 1).
Data collection The study collected data from workers related to age, period of combined exposure to noise and hydrocarbons and the results of reference pure tone audiometry.
Chart 1. Classification of the degree of hearing loss according to the WHO(23) Degree of hearing loss
Mean ISO value
Normal
0 to 25 dBNA
Mild
26 to 40 dBNA
Moderate
41 to 60 dBNA
Severe
61 to 80 dBNA
Deep
≥ 81 dBNA
Data analysis Due to the large number of drawn hearing thresholds in multiples of five, the survival for grouped data was the most adequate statistical model for this study(19). The investigation also analyzed hearing thresholds at frequencies of 500, 1000, 2000 and 4000 Hz, to score the degree of hearing loss. The importance to analyze thresholds at frequencies of 6000 Hz in studies involving exposure to ototoxic agents is well known, since they are often affected in this type of hearing loss (noise and/or chemicals), and 8000 Hz, which may be influenced by age (presbycusis). However, aiming to address the internationally standardized criterion to score the degree of hearing loss(20), these frequencies were not considered in the statistical analysis. The present results may also raise reflections on the scoring of degree of hearing loss in cases of exposure to ototoxic agents. Considering the ratio of expressive draws equal to 0.80, the discrete model was adequate to determine the hearing threshold. Also, due to the low frequency in some intervals, the hearing thresholds were grouped in intervals of (0,15], (15,20], (20,25] and (25,45], for both ears. The adjusted models were the classical discrete models of proportional risk and Colosimo’s logistic(19), which model the conditional likelihood of not detecting the stimulus in a given time period, if the individual detected it in previous intervals. The models further considered the covariables age and period of exposure and the interaction between them. The proportional risk model was adjusted using linearization of conditional probability, according to the covariables. Estimate of the logistic model was performed by logit transformation, which is a logarithm of the ratio of conditional probabilities. Both adjustments may be done only numerically and with the aid of softwares. The Bayesian Information Criterion of Schwarz (BIC) was applied for selection between the two models (proportional risk and logistic). This criterion assumes a true model, which describes the relationship between hearing threshold and the independent variables (age and period of exposure), between the two models proposed. Therefore, the criterion is based Audiol Commun Res. 2015;20(4):313-20
Data were processed and analyzed on the software Microsoft Office Professional Plus 2013 and the software R, version 2.12.2.
RESULTS Characterization of the sample regarding the hearing thresholds for frequencies of 500 to 4000 Hz, for the right and left ears, respectively, is presented in Tables 1 and 2. Table 1. Sample characterization according to the hearing thresholds for frequencies of 500 to 4000 Hz, on the right ear Hearing threshold (dB)
500 Hz
1000 Hz
2000 Hz
4000 Hz
0 to 15
10
16
15
9
15 to 20
4
4
5
4
20 to 25
4
3
2
5
25 to 45
3
2
3
7
Total number of individuals
25
25
25
25
Table 2. Sample characterization according to the hearing thresholds for frequencies of 500 to 4000 Hz, on the left ear Hearing threshold (dB)
500 Hz
1000 Hz
2000 Hz
4000 Hz
0 to 15
11
18
16
8
15 to 20
7
6
7
6
20 to 25
5
1
1
4
25 to 45
2
0
1
7
Total number of individuals
25
25
25
25
315
Fernandes R, Tsunemi MH, Zucki F
Table 3. Proportional risk and logistic models for the hearing thresholds on the right ear CV
DF
Proportional risk
Logistic
LRT
p-value
LRT
p-value
0 to 15
1
7.59
0.536
0.72
0.810
15 to 20
1
1.64
0.328
12.20
0.119
20 to 25
1
17.07
0.062
41.78
0.016*
25 to 45
1
24.43
0.046*
54.09
0.011*
Age
1
0.12
0.576
0.33
0.576
Exposure
1
0.02
0.642
0.07
0.948
Age exposure
1
0.28
0.609
0.02
0.882
*Significant values (p
